Gas cushion keep-alive electrode



March 6, 1962 D. L. SCHAEFER ETAL 3,024,382

GAS CUSHION KEEP-ALIVE ELECTRODE Filed Sept. 4, 1959 INVENTORS DONALD L.SCHAEFER JOHN E. WHITE BY A ITOR/VEYS United States are-tit 3,924,382Patented Mar. 6, 1962 This invention relates to gaseous dischargedevices, and more particularly to the rapid ignition, and mainvtenanceof the main discharge of a cold cathode gaseous device by anauxiliaryelectrode.

Gas or vapor-filled electron tubes may generally be classified as to thetype of cathode employed, namely hot or cold. Each type may vary as tothe number of .electrodes and further, the cathods themselves may beeither liquid or solid. These electron tubes find their principal use asrectifiers, voltage regulators, control devices, switches, sweep circuitoscillators and in recent times as modulator and T.-R. tubes withinradar systems. Cold cathode tubes such as those employing a mercury poolafford certain advantages over hot cathode tubes. Certain vapor or gasfilled tubes are provided with keepalive electrodes which continuouslymaintain an arc to the cathode. Suchkeep-alive electrodes are necessaryin single anode mercury-cathode units where the tube would otherwiseextinguish during the negative half cycle of an applied AC. voltage, orwhere the anode voltage was momentarily interrupted, or where the anodecurrent is pulsed. Ignition methods such as the production of a highfield by an auxiliary electrode closely spaced above a mercury cathodepool has proved impractical because of the waves and fluctuations in themercury pool level of liquid cathode tubes, and the erosion of cathodematerials in solid cathode tubes.

The desirable electrical characteristics of cold liquid cathode gas orvapor tubes can be put to many useful purposes as for example, in pulsemodulator tubes and T.-R. tubes where a single anode is employed sincehigh current pulse application is possible and the cold cathode tube isnot subject to the current density limitations of thermionic cathodes inapplication. However, before this type of cold liquid'cathode tube maybe used successfully, a method for igniting and maintaining a cathodespot is essential.

It is therefore an object of this invention to provide a device forigniting and maintaining a cathode spot on liquid cathodes of gas orvapor-filled electronic tubes.

Another object is to provide a device for creating a continuous supplyof electrons from a liquid cathode sufiicient to ignite the main are ofa tube.

A further object is to provide a relatively low current .drain devicefor the ignition of a liquid cold cathode gas tube.

Other objects are to provide an electrically and mechanically simple,efiicient, inexpensive and reliable device for the ignition of liquidcold cathode gas tubes.

Other objects and advantages will be apparent from the followingdescription of embodiments of the invention and the novel .featuresthereof will be particularly pointed out hereinafter in connection withthe appended claims.

In the accompanying drawings:

FIG. 1 is a cross-sectional diagram of a liquid cathode tubeillustrating an embodiment of the invention; and

FIG. 2 is a perspective, illustrating another embodiment of theinvention.

In the embodiment of the invention illustrated in FIG. 1, a closed glassenvelope 1, or an envelope of, any suitable material, contains a vaporor gas filling, an anode 2. supported therein by conducting rod 3, and aliquid mercury pool cathode 4 or a gallium pool disposed at the base ofthe envelope or tube opposite the anode. Electrical connection fromoutside the envelope is made to the anode through the electricalconducting rod 3 which extends from, and'is secured to, the anode andpasses through that portion of the envelope opposite and remote from thecathode for external wiring thereto. Conducting rods 5 and 6 extendthrough a portion of the base of the envelope into the liquid cathode 4,and electrical connection from the exterior of the envelope is made tothe cathode by means of these rods. The ends of the rods disposed withinthe cathode project into the cathode from the base of the envelope andextend upwardly to an area well below the surface of the cathode.Electrical lead-in rods 7, and 8 extend and project through oppositevertical side walls of the envelope in a direction normal to the sidesat points intermediate between the surface of the cathode and the anode,and their inner end portions are threaded. Since the tube is vapor orgas filled, the rods 3, 5, 6, 7 and 8 are peripherically bonded to theenvelope wall through which they pass so as to hermetically seal theenvelope which is evacuated and filled with a suitable ionizable gas orvapor, such as mercury. Retaining nuts 10 and 11 are threaded on the endportions 9 of each of the lead-in rods 7 and 8 and a sickle shaped tab12 is supported between the tightly abutting faces of each pair of thesenuts. The concave portions of these tabs face each other and meet anyspring-like, electrically conductive, heat resistant material, such asfor example. molybdenum. Each tab 12 may be afiixed to its lead in rodin any suitable manner providing the end of the tab so afiixed ispermanently tightly confined against movement. A wire 13 of a materialwhich will withstand high temperatures, having intermediate of its endsa horizontally undulatory portion 13a, such as of S shape is welded orotherwise firmly fixed to the free ends of the tabs to connect them. Thetabs 12 support the wire 13, which may be, for example, of tungsten ormolybdenum just above and spaced slightly from the mercury cathode, withthe plane of the 8 portion of the wire parallel to the cathode surface,and by reason of the arouate form and resiliency of the tabs, is movablea short distance toward and away from the cathode surface when subjectedto opposing forces. The S shape of the wire 13, by giving extraconcentration of weight in a local zone of the wire, gives the wirefreedom of motion and causes the 8 portion of the wire to sag in thedirection of the cathode surface.

When a DC. potential is applied, as by battery 14, between thekeep-alive wire 13 and the mercury cathode, the keep-alive wire beingpositive with respect to the cathode, the keep-alive wire automaticallyadjusts itself in spaced relation to the cathode surface under theaction of two oppositely directed forces. The electrostatic forcecreated by theapplied DC. potential tends to pull the wire in thedirection of the mercury cathode, but as the wire approaches the cathodesurface arcing ensues be tween the wire and the cathode, and a cathodespot forms on the cathode surface directlyopposit'e the wire. With theformation of the arc, a vapor blast or a Tanberg effect occurs whichapplies a repulsive or upwardly directed force to that portion of thewire directly above the cathode spot. The electrostatic and the vaporblast forces act on the wire in opposing directions and the Wiretherefore automatically assumes a spaced relation above the cathodesurface whereat these forces are equal and opposite so that thekeep-alive wire is in mechanical and physical equilibrium. Under theseconditions, an arc is continually maintained between the keep-alive wireelectrode and the liquid cathode. The spacing between the keep-alivewire electrode is thus automatically adjusted to maintain the arc. Ifthe DC. potential should decrease or temporarily extinguish thekeep-alive wire would then move toward the cathode until either thespacing between the wire and the cathode was sufiicient to reignite theare or until its movement toward the cathode was mechanically limited bythe tabs 12 and then when the DC. potential was again applied the arcwould reignite and the wire 13 would again be repelled from the cathodesurface by the vapor blast until it again assumed its equilibrium orfiring position.

It has been found that successful operation under the above conditionscan be maintained using a 0.0008 inch tungsten wire 13 tabed with a0.001 inch thick tab 12, 0.005 inch wide and about one millimeter long.The keep-alive arc provides the necessary vapor ionization, thoughlocalized, in the tube so that when a voltage is applied between themain anode 2 and cathode 4, a main discharge or conduction will beaccurate, reliable and immediate.

A third electrode, as for example a control grid (not shown), may beadded to the above described tube embodiment. This arrangement is theequivalent of a thyratron tube with a cold liquid cathode and isextremely useful for pulse-modulation applications since the anodecurrent exceeds that of the solid cathode thyratron.

In an embodiment of another keep-alive electrode according to thisinvention, which is illustrated in FIG. 2, a metallic horizontal supportextends across the tube chamber, with its ends passing through andsealed to opposite walls of the tube 10, and within the tube chamber ithas two substantially parallel. depending metallic hangers 21 and 22,spaced from each other. The free ends of the hangers are bent back onthemselves to form hanger eyes 23 and 24 whose openings are axiallyaligned with one another and receive therein and support therebetweenfor axial rotation, a cylindrical metallic rod 25. Disposed incross-wise relation to the cylindrical rod 25 and suitably secured orspot welded at the approximate center of the rod 25 is a metallic vane26. The vane is secured to the rod at approximately the vanes center ofgravity 27, so that the vane is balanced about the point of contact, andsince rod 25 is free to rotate the vane 26 can pivot about the axis ofrod 25 somewhat like a scale balance. One end portion of the vane 23 isspoon shaped with the concave side facing upwardly, such assubstantially in the direction of the support 20, while the opposite endportion 29 of the vane is bent upwardly and laterally as at 29, to forman offset end 29a which is approximately parallel with the main body ofthe vane. This upwardly offset end of the vane extends between andbeyond the arms 30 and 31 of a U-shaped member 32, that areperpendicular to the plane of the vane and substantially parallel to thehangers, thereby limiting the pivoting motion of the vane to withinselected limits. One arm of the member 32, as for instance arm 31, isextended and bent, and then attached, as by spot welding, to one of thehangers 22 for support. This entire keep-alive structure is supportedwithin the closed gas-filled envelope or tube in so that the spoonportion 28 of the vane in its lowermost position of travel is disposedjust above the surface of the liquid cathode.

The operation of this balanced vane keep-alive is similar to theoperation of the first described embodiment, except that the verticaltravel of the spoon or electrode is limited by the U-shaped member 32and a larger electrode (spoon) surface is employed. The componentmembers of this last described embodiment preferably should be oftantalum or tungsten or a combination thereof. The DC. potential isapplied between the cathode and the ends 33 and 34 of the supportoutside of the tube envelope. Since all the keep-alive components areelectrical conductors, this DC. potential also exists between the vane26 and the cathode.

The keep-alive devices described herein when used with liquid coldcathodes are means to supply a virtually unlimited electron source fortubes such as pulse modulators, and these cold cathode tubes are alsovaluable where high current pulse applications are required. Comparisonwith competitive devices such as thyratrons, ignitrons and excitronswill bear out the advantages of this keepalive electrode. Ignoring thesimplicity and the lower cost of operation of the gas cushionkeep-alive, it is capable of withstanding overload and fault currentsover those of a thyratron. Commercial thyratrons will generally deliverabout 1 ampere peak per watt of cathode heating power while the gascushion keep-alive can operate from a volt source at 10 milliamperes.Comparison with an ignitron is quite favorable, since a tube employingthe keep-alive embodiment of this invention has all the advantages ofhigh peak anode currents, with low control power of a grid as comparedto the tens of amperes at hundreds of volts required by the ignitron.Comparison with the excitron or multianode rectifier shows immediatelythe advantage of substantially lower excitation power and moreover, thekeep-alive restrains the motion of the cathode spot to a small areadirectly below the keep-alive electrode, so that the major problem ofexcitron and multi-anode tube design, that of keeping the cathode spotoff the tube walls, is avoided.

It will be understood that various other changes in the details,materials and the arrangements of parts which have been herein describedand illustrated in order to explain the nature of this invention, may bemade by those skilled in the art within the principle and scope of theinvention as expressed in the appended claims.

We claim:

1. A gaseous electric discharge device comprising a closed envelopecontaining a gas filling and having therein spaced relation to oneanother, an anode and a liquid cathode with a surface exposed towardsaid anode, an auxiliary electrode device disposed in said envelopebetween the anode and said cathode surface but with a part thereof inclose proximity to the cathode, that is movable toward and away fromsaid exposed cathode surface under relatively small vapor blast andelectrostatic forces but limited against contact with said cathodesurface whereby when a potential is created between said electrode partand said cathode surface, said electrode part will be in mechanicalphysical equilibrium in spaced relation to the cathode surface due tothe opposing forces created by the electrostatic attractive forcepulling said electrode part toward the cathode and the opposing vaporblast rcpulsing force from the cathode facilitating thereby theestablishment and maintenance of the main discharge between said anodeand said cathode.

2. The device according to claim 1, wherein said closed envelopecontains mercury vapor and said liquid cathode is mercury.

33. The device according to claim 1, wherein said closed envelopecontains another electrode disposed between said auxiliary electrode andsaid anode for control of said main discharge.

4. The device according to claim 1, wherein said auxiliary electrode isa bar physically supported and balanced for pivotal movement whereby itsends are movable toward and away from said exposed cathode surface.

5. The device according to claim 4, wherein an end of said bar has alarge surface area directed substantially toward said cathode.

6. A gaseous electric discharge device comprising a closed envelopecontaining a gas filling and having therein in spaced relation to oneanother, an anode and a liquid cathode with a surface exposed towardsaid anode, an auxiliary electrode device disposed in said envelopebetween the anode and said cathode surface but with a part thereof inclose proximity to the cathode, said auxiliary electrode being arelatively fine wire supported at its ends to close proximity to thecathode, that is movable toward and away from said exposed cathodesurface under relatively small forces but limited against contact withsaid cathode surface whereby when a potential is created between saidelectrode part and said cathode surface, said electrode part will be inmechanical physical equilibrium in spaced relation to the cathodesurface due to the opposing forces created by the electrostaticattractive force pulling said electrode part toward the cathode and theopposing vapor blast repulsing force from the cathode facilitatingthereby the establishment and maintenance of the main discharge betweensaid anode and said cathode.

7. The device according to claim 6, wherein said fine wire has anundulatory portion plane which is substantially parallel to said cathodesurface.

8. The device according to claim 7, wherein said undulatory portion ofsaid wire is S shaped.

References Cited in the file of this patent UNITED STATES PATENTS

